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This sets mac address using ip set link mac.

This can help break ties consistently when multiple events have the same
timestamp.

Also splits out arg parsing from running so code can use the mac address in
initializationg before calling run.

for no_simbricks experiments

This changed a while ago in one of the refactoring steps so some of the scripts
were broken.

- adds description for netperf experiment
- reformat local.py
- reformat results/netperf.py

- classes ExpEnv and ExpOutput had to be moved to prevent circular imports
- reformat common.py